The present invention is concerned with a beating element for grinding apparatus for fibrous, preferably vegetable material, which element comprising a supporting component and, attached thereto, at least one ring of segment plates of some hard material which form the grinding surface of the element. In a design commonly met with, such beating elements are given the form of a disc with the segment plates mounted in one or more concentric rings on the radial face of the disc-shaped supporting element. The grinding apparatus is equipped with at least two grinding discs held under pressure the one against the other and mutually rotatable, the feed stock, such as wood chips, being finely divided in the gap between the discs. This gap is defined by the grinding plates. The surface of these plates, which face each other, carrier a relief pattern of ribs and ridges, or similar raised surface, to facilitate the process of beating or defibrating the material and separating its fibres and fibrils. In modern beating equipment, the grinding disc rotates at high speed and, furthermore, its diameter is large, and consequently the centrifugal force acting on the plates is extremely strong. By way of illustration it may be noted that in plates weighing only some few tens of kilograms, centrifugal forces in the region of 50 tons may occur.
Hitherto the grinding plates have been secured to the disc-shaped supporting element or grinding-disc holder by bolting, the bolts being screwed into the plates from behind. Since a very high degree of stress has to be reckoned with, several bolts are used for attaching each plate, but in spite of this the stress occurring in the plate itself remains so great that the plates must be designed to a thickness, and therefore to a weight, far in excess of what is actually required for the provision of surface ribs and ridges. In addition, in order to render the plates as resistant as possible to wear, they must be made of extremely hard material, the strength of which is not easily estimated in design calculation. In other words, the design size of the plates is far too large, and therefore the stress to which they and the bolts attaching them to the disc are subjected is increased still further; and because of the great thickness of the plates the centrifugal force to which they are exposed also develops strong torque around their outer circumference and strives to hurl the plates outwards from the supporting disc.